Phonon-assisted anti-Stokes photoluminescence (ASPL) up-conversion lies at the heart of optical refrigeration in solids. The thermal energy contained in the lattice vibrations is taken away by the emitted anti-Stokes photons’ ASPL process, resulting in laser cooling of solids. To date, net laser cooling of solids is limited in rare-earth (RE)-doped crystals, glasses, and direct band gap semiconductors. Searching more solid materials with efficient phonon-assisted photoluminescence up-conversion is important to enrich optical refrigeration research. Here, we demonstrate the phonon-assisted PL up-conversion process from the silicon vacancy (SiV) center in diamond for the first time by studying ASPL spectra for the dependence of temperature, laser power, and excitation energy. Although net cooling has not been observed, our results show that net laser cooling might be eventually achieved in diamond by improving the external quantum efficiency to higher than 95%. Our work provides a promising route to investigate the laser cooling effect in diamond.

The solid state single photon source is fundamental key device for application of quantum communication, quantum computing, quantum information and quantum precious metrology. After years of searching, researchers have found the single photon emitters in zero-dimensional quantum dots (QDs), one-dimensional nanowires, three-dimensional wide bandgap materials, as well as two-dimensional (2D) materials developed recently. Here we will give a brief review on the single photon emitters in 2D van der Waals materials. We will firstly introduce the quantum emitters from various 2D materials and their characteristics. Then we will introduce the electrically driven quantum light in the transition metal dichalcogenides (TMDs)-based light emitting diode (LED). In addition, we will introduce how to tailor the quantum emitters by nanopillars and strain engineering, the entanglement between chiral phonons (CPs) and single photon in monolayer TMDs. Finally, we will give a perspective on the opportunities and challenges of 2D materials-based quantum light sources.